This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Contraception provides significant preventative health benefits by reducing unintended pregnancy, abortions, and unwanted births. As side effects, access, and cultural or moral objections limit the universal acceptance of current methods, research into novel contraceptives is warranted. The purpose of this project is to explore the hypotheses that selective expression of phosphodiesterase (PDE) isoforms exists in the primate ovary, that selective blockade of the PDE3 isoform can be exploited to prevent spontaneous and gonadotropin-induced oocyte maturation, and that chronic treatment with a PDE3 inhibitor can prevent pregnancy in primates without affecting menstrual cyclicity or luteal function. The Specific Aims are to: (1) describe the basic biology of PDE expression in the primate ovary, (2) determine if PDE3 inhibitors prevent oocyte maturation, but not ovulation and function of the corpus luteum in rhesus monkeys undergoing controlled ovarian stimulation (COS) protocols or during natural cycles in vivo, and 3) determine whether PDE3 inhibitors function as contraceptive agents in regularly cycling rhesus monkeys in paired mating situations. In the final year of the grant, attention was also directed to the role of cGMP-medicated regulation of PDE3.